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Should be another easy one here, but I need clarification on what they define as "heavy utilization" for Reserved Instance types. From their Website:

Heavy Utilization RIs – Heavy Utilization RIs offer the most absolute savings of any Reserved Instance type. They’re most appropriate for steady-state workloads where you’re willing to commit to always running these instances in exchange for our lowest hourly usage fee. With this RI, you pay a little higher upfront payment than Medium Utilization RIs, a significantly lower hourly usage fee, and you’re charged that lower hourly rate for every hour in the Reserved Instance term you purchase. Using Heavy Utilization RIs, you can save up to 41% for a 1-year term and 58% for a 3-year term vs. running On-Demand Instances. If you’re trying to find a break-even utilization, you’re economically advantaged using Heavy Utilization RIs (vs. On-Demand Instances) if you plan to use your instance more than 43% of a 1-year term or 79% of a 3-year term.

I'm assuming that, if I'm planning on running a 24/7 Web Server, then regardless of how many resources I consume (bandwidth, cpu cycles, memory), I would want to go with a Heavy Utilization Reserved Instance? This one Web Server in particular will likely barely budge the cpu, but it needs to be up and running 24/7.

Not 100% on what they're defining as "heavy".

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3 Answers 3

up vote 22 down vote accepted

Heavy refers to how much of a month the instance is turned on, not the CPU load, so yes, any 24/7 server would be "heavy utilization".

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3  
They really need to add text to that effect on the pricing page. –  Jason Axelson Jun 27 '12 at 9:08
    
As noted in the comments to other answers, unlike light or medium utilization, you must also pay the hourly fees 24/7, even when you do not have any instance running. –  Antti Haapala Mar 31 at 14:13

Another way to view the utilization rates above is in terms of aggregate usage. If you purchase a 3-year term Medium Reserved Instance, you need only run that instance for a total of 8.7 months over the course of the 3-year term (24% of the term) for your costs to equal those of On-Demand. Any usage beyond this amount incrementally increases your savings.

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Good point, afa-at-work. –  gravyface Feb 14 '12 at 20:47

The difference is this.

If you purchase a Heavy Utilization instance you have already pre-paid in full the discounted hourly rate for this server even if you turn it off. By using Heavy Utilization your telling amazon that you will be using this 24/7 365 days a year.

The other levels, Light and Medium do not charge you the hourly rate while you're not using the server and your pre-paid discounted amount is lower based on that assumption. Lets take for example the following.

Heavy utilization

732hr/mo Light Utilization m1.small $97.50 (one time fee) + $438 hourly $535.50 / yr
732hr/mo Heavy Utilization m1.small $276.25 (one time fee) + $175.20 hourly $451.45 / yr

366hr/mo Light Utilization m1.small $97.50 (one time fee) + $219.60 hourly $317.10 / yr
366hr/mo Heavy Utilization m1.small $276.25 (one time fee) + $175.20 hourly $451.45 / yr

Notice that no matter how many hours you use the heavy utilization you get charged the same per year. The other levels allow you to take advantage of the reserved instances without using the instance 24/7.

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This is just plain wrong, to my knowledge. No, you don't pay the hourly rate if it's turned off. –  ceejayoz Jun 25 '12 at 2:50
7  
This is accurate. You pay for the hourly rate even when turned off for the Heavy Utilization. Please check your facts. Quote from amazons page "Heavy Utilization Reserved Instances are billed for every hour during the entire Reserved Instance term (which means you’re charged the hourly fee regardless of whether any usage has occurred during an hour)." aws.amazon.com/ec2/#pricing –  bwight Jun 25 '12 at 18:22

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